In a digital communication system, frequency selectivity and time fluctuation of a transmission line occur because of multipath fading caused by reflection of a transmission signal on a building or the like and Doppler fluctuation caused by movement of a terminal. In such a multipath environment, a reception signal is a signal in which a transmission symbol and a symbol reaching after a delay time interfere with each other.
A single carrier block transmission system for obtaining a best reception characteristic in such a transmission line having the frequency selectivity attracts attention in recent years (see, for example, Non Patent Literature 1 described below). In the single carrier (SC) block transmission system, peak power can be set low compared with an OFDM (Orthogonal Frequency Division Multiplexing) transmission system (see, for example, Non Patent Literature 2 described below), which is a multiple carrier (MC) block transmission.
In a transmitter that performs SC block transmission, for example, a measure against the multipath fading is taken by performing transmission explained below. First, a PSK (Phase Shift Keying) signal and QAM (Quadrature Amplitude Modulation) signal, which are digital modulation signals, are generated in a “Modulator”. Then, the digital modulation signals are converted into time domain signals by a pre-coder and an IDFT (Inverse Discrete Fourier Transform) processing unit. The PSK and QAM signals are generated by bit sequences generated using an interleaver that arranges the bit sequences in discontinuous forms of error correction codes and bits in times, frequencies, and the like. As the error correction codes, there are a convolutional code, a turbo code, an LDPC (Low Density Parity Check) code, and the like, which are generally used. Thereafter, as a measure against the multipath fading, a CP is inserted in a CP (Cyclic Prefix) inserting unit. The CP inserting unit copies a predetermined number of samples after the time domain signals and adds the samples to the beginning of a transmission signal. Besides, as a measure against the multipath fading, ZP (zero padding) for inserting zero in a portion of the beginning or the end of data is performed.
To suppress transmission peak power, in the transmitter that performs the SC transmission, in general, OFT (Discrete Fourier Transform) processing is performed by the pre-coder. Besides, there is also an example in which a pre-coder or the like employing a unitary matrix is used (see, for example, Non Patent Literature 3 described below).